Look, I may be in a minority here with all you rugged individualists, but protecting the safety and well-being of those he is leading and getting them back to the boat safely is the DM's #1 job. Sure, sometimes you need the expert fish-spotter more than you need the lifesaver, and it's great when the DM has a sense of humor, but let's not kid ourselves which is the most important ability in a DM. They are, after all, certified in rescue for a reason.
Last year in Palau, I got a leak in my air hose. No biggie, it wasn't leaking that fast, easy conditions, and my son and husband were with me. But the DM hovered around me like I was a newly-hatched chick. Personally, I found that reassuring rather than annoying. I was a potential catastrophe and he dealt with it. Awesome.
I like what (Chief?) said:
As for the DM, I would say I think divers should be *prepared* to have a DM who is useless for their safety, but they should EXPECT a DM who puts their safety and care at the top of the list. I don't think a tour guide only DM is acceptable.